Dual-mode X-Band EPR and magnetic study of (Cu2+, Ln3+) pairs: Investigation of magnetic anisotropy

An experimental and theoretical approach for the determination of the anisotropic exchange interaction constants in (Cu2+, Ln3+) pairs where Ln = Tb3+, Dy3+ is presented. According to this approach the same phenomenological anisotropic magnetic model was used to simulate the low temperature magnetic behaviour of the pairs as well as their EPR spectra in parallel and perpendicular mode. For the (Cu, Tb), [L1Cu(O2COMe)Tb(thd)2], (L1 = N,N′-2,2-dimethylpropylenedi(3-methoxysalicylideneiminato; thd- = tetramethylheptanedionato)) and (Cu, Dy) complexes, [L2Cu-(Me2CO)Ln(NO3)3], (L2 = N,N′-2-methyl-1,2-propylenedi(3-methoxysalicylideneiminato)), it has been found that the exchange interaction is ferromagnetic with the Jz interaction component larger than the other two terms (Jz ≫ Jx ∼ Jy). In order to determine the zero-field splitting of the high-spin ground state S = 4 in two ferromagnetic-coupled (Cu, Gd) pairs, [L1Cu(O2COMe)Gd(thd)2] and [L2Cu(Me2CO)Gd(NO3)3], the EPR spectra in parallel mode were simulated with an appropriate magnetic model. Indeed, one of the most important problems concerning the (Cu, Gd) systems is the complexity of the X-band, perpendicular-mode EPR spectra that renders any simulation procedure difficult. Improvement in analysis of the spectra results from using parallel mode EPR experiments.